A broadcasting network to which the invention is applicable can be a one-way network and transmit service signals to all of the user devices connected to the network, certain services being accessible only as a function of an access right. The applications that are the most well known are broadcasting of television and/or radio-broadcasting signals, e.g. via a data broadcasting network of any of the following types: DVB (Digital Video Broadcasting), DAB (Digital Audio Broadcasting), DMB (Digital Multimedia Broadcasting), DTT or DTTV (Digital Terrestrial Television), ISDB-T (Integrated Services Digital Broadcasting-Terrestrial), MBMS (Multimedia Broadcast Multicast Service) and BCMCS (Broadcast Multicast Service) over mobile telephone networks such as third-generation or fourth-generation mobile telephone networks etc., or the Internet. In another example, a Wireless Local Area Network (WLAN) can be used as the broadcasting network. The invention also applies to the system defined by the OMA-BCAST (Open Mobile Alliance-Broadcast) specification.
A broadcasting channel of a broadcasting network transmits a number of services that varies as a function of the passband available for transmitting data. In order to enable a user to discover all of the services broadcast via the broadcasting network, at least one description service for describing the broadcast services and referred to as an “Electronic Service Guide” (ESG) is proposed. The description service is broadcast by the broadcasting network, or transmitted by a point-to-point telecommunications network such as a cellular radiocommunications network, to user mobile terminals at their request.
The electronic service guide contains various information about the services broadcast by the broadcasting network. Those services are, for example, television programs including, in particular, films, documentaries, and/or magazines. The electronic service guide constitutes the point of access to the services that are broadcast more particularly for the user of a mobile terminal. Depending on the information in the guide, users select a service that they wish to obtain, e.g. for viewing purposes. The service guide also has service description information such as an associated rating code or an identifier of the service provider.
Giving access to the services broadcast by the broadcasting network for all audiences goes against restricting viewing of services that are for viewing by one category of users only.
For example, a child can then view a service that is intended exclusively for adults.
In another example, certain services are broadcast by an operator who is a competitor of the initial operator whom the user chose and who supplied the terminal device to said user. The initial operator can then not restrict the available services to only those services that it provides and/or that are provided by a partner.
In order to mitigate those drawbacks, a “Conditional Access System” (CAS) or “Key Management System” (KMS) supplied by a service broadcasting operator makes service viewing on a terminal device conditional upon possessing a right of access to the services that the operator is broadcasting. Those services are encrypted before being broadcast over the broadcasting network. In order to view the service, the user must first purchase access rights, represented in the form of decryption keys, from the operator who is offering the service.
Unfortunately, no protection prevents viewing of certain services that are broadcast unencrypted over the broadcasting network but that are unsuitable, for example, for children.
There is thus a need to have a protection system that is capable of enabling a possessor of a terminal device to restrict viewing of services broadcast unencrypted over a broadcasting network.
In addition, such conditional access systems generally act on services that are broadcast in ordinary mode. Ordinary broadcasting requires all of the services broadcast over the network to be processed by a terminal device before the desired broadcast service(s) is/are selected, such processing requiring considerable real-time processing capacity.